Dept. of Dermatology - University of Iowa College of Medicine
 Dermatology Differential Diagnosis by Morphology
Thomas L. Ray, M.D.
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This resource is not a diagnostic system ! It is not intended to be used as artificial intelligence !
The sole purpose of Dermatology Differential Diagnosis by Morphology is to assist students and residents of dermatology in learning differential diagnoses of skin disorders and diseases. Based on clinical and morphologic appearances of primary and secondary skin lesions, lists of potential diagnoses are given for major types of skin lesions. The lists are modified by additional characteristics which may be present.
Definitions of primary and secondary skin lesions may be found by clicking on the appropriate heading. Additional information and examples may be found in An Introduction to Basic Dermatology by Dr. Warren Piette and the Image Database. In some browsers (i.e. Netscape 2.0 and later), this will open as a new browser window, so both files can be viewed simultaneously. Selected diagnoses in the database are also linked to examples in this presentation. When finished with an example, the user should close the extra window(s), before proceeding.
To explore differential diagnoses of skin lesions, select and click on a morphologic feature, then select and click on a modifying feature that will be presented in subsequent tables. Click on selected diagnoses (and subsequent numbers) to access clinical images of the entity. Each images will open as a new browser window, so that multiple images can be viewed simultaneously. Close the additional "new" windows when finished.
In order for lists of differential diagnoses to be practical and useful, the disorders given are limited to characteristic, typical entities commonly presenting with a morphologic feature. Thus, the diagnoses provided are not exhaustive or comprehensive lists. They are not all inclusive (nor exclusive) of other diseases or conditions that may present with (or without) similar morphologic features.
This resource is not a diagnostic system ! It is not intended to be used as artificial intelligence !
Please read and abide by the disclaimer and copyright statements.
- If you have questions about skin lesions or diseases, consult a dermatologist. Inquiries to this WebSite about skin disease entities will not be answered. If you seek additional information, try searching the WWW, or consult a dermatology textbook, readily available at a medical library. A medical librarian can help you find the material you seek.
There are no universally agreed upon definitions of terms or, in particular, dimensions of primary lesions. The following was offered by Watt and Jillson* as an "easy-to-remember" formula.
- Macule - circumscribed area of skin, up to 1.0 cm, with a change from normal skin color, which is neither raised above nor depressed below the surrounding skin. Many use the term for lesions much greater than 1.0 cm. Term does not include purpura.
Patch - a flat, circumscribed, discoloration of skin or mucous membrane greater than 1.0 cm in diameter.
- Papule - discrete solid area of skin that is elevated by palpation above the surrounding skin and less than 1 cm in diameter. Variations include accuminate, keratotic, flat-topped, follicular, umbilicated, pedunculated, necrotitic and others.
Plaque - similar to a papule but greater that 1.0 cm in diameter. Often formed by the confluence or coalescence of papules. Secondary features may include, among others, atrophy, lichenification or hyperkeratosis.
- Nodule - descrete, solid, palpable, round or oval (elipsoidal) lesion of the skin measuring up to 1.0 cm in diameter (or long axis). Applies to processes involving any or all levels of the skin, and is a general term for any mass, benign or malignant.
- Tumor - a term used by some for a "nodule" greater than 1.0 cm in diameter. Applies to processes involving any or all levels of the skin, and is a general term for any mass, benign or malignant.
- Vesicle - a circumscribed fluid-filled lesion less than 1.0 cm in diameter that is usually elevated above the surrounding skin. May be described as solitary, grouped, umbilicated, dyshidrotic, spongiotic, multi-locular or uni-locular.
- Bulla - a circumscribed fluid-filled lesion greater than 1.0 cm in diameter that is usually elevated above the surrounding skin. May attain diameters of several cms and are described as tense, or flacid.
- Pustule - descrete elevated vesicle or bulla of skin, usually small, containing purulent exudate composed of inflammatory leukocytes (pus), with or without cellular debris. May be superficial, deep-seated, follicular, grouped, etc. and may arise secondarily from a vesicle.
- Wheal - an evanescent, round or irregular, often flat-topped elevation of skin with a pale red color, arising from edema in the superficial dermis. May vary from 2-3 mm to 10 or more cm in diameter, with round or arcuate configurations. Should be distinguished from angioedema, a massive edema involving the entire dermis and subcutaneous tissues.
- Scar - a hard plaque of dense fibrotic tissue covered by a thin epidermis. A mark of injury from any sort of process (physical or pathologic).
- Atrophy - Atrophy usually refers to thinning of the epidermis leaving an easily wrinkled and/or shiny surface. Atrophy may also apply to dermal and/or subcutaneous tissue, with or without changes in the epidermis.
- Ulcer - loss of skin tissue or substance from the surface downward, leaving an uncovered or denuded wound that is slow to heal.
- Erosion - a superficial denudation of the skin, usually implying the loss of the epidermis.
- Fissure - a vertical splitting or separation of the skin.
- Crust - dried surface fluid, often serous (inspissated serum) in nature, with or without tissue debris. For purposes of this document this includes the term "scab".
- Excoriation - a scratch mark, often with denudation of the skin to form a small ulcer. Exposure of the corium by mechanical removal of the epidermis.
- Scale - a thin flake of epithelium (mostly composed of corneoctyes) which is separated from the underlying intact skin proper.
- Lichenification - a thickening of the skin surface and an increase of skin markings, usually seen with chronic coalescence of papular lesions, especially atopic eczema.
- Vegetating - a lushly growing, proliferating, process, usually with elevated or exophytic features.
- Linear / Figurate - technically not secondary features, but included here solely out of convenience. These are configurations that skin lesions may assume, which aid in their diagnostic identification. Figurate includes geometrical shapes (e.g. annular, arciform, cyclic, etc.).
Watt, T.L. and Jillson, O.F.: Archives of Dermatology 90:454, 1964.
Created June, 1996
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Last updated January 29, 2004